| For the problem that MOV was destructed under at a waveform of 10/350 μs and 8/20μs, the paper used scanning electron microscopy (SEM) combined with material composition analysis X-ray diffraction (XRD) for the study of accompanying changes of materials in zinc oxide varistor during a high voltage impact process and investigated the MOV destruction mechanism under the surge impact from the perspective of microstructure and composition. Studies have shown that in the late stage of the impact destruction of 8/20 μs waveform, the control ability of Sb2O3 in the MOV on the overall compactness decreased significantly, the internal grain size increased, and there were characteristics of squeezing destruction between crystal interfaces. A large amount of heat would cause the Bi2O3 in the MOV to gradually volatilized during the destruction process of the impact of waveform at 10/350 μs, resulting in uneven MOV internal ion transport. The 8/20 μs waveform impact destructed and damaged MOV internal microstructure did not necessarily change a lot and the damaged extent was related with the number of impact. But no matter what type of impact destruction was, the MOV destruction essence was the internal microscopic substance was gradually transformed from crystalline state into semi-crystalline state process.For the destruction problem of MOV at a single-time of 8/20 μs waveform and the same time sequence repeatedly pulse impact, the study based on the multi-pulse impact platform of Lightning Protection Center of Heilongjiang Province, used XRD-Rietveld whole spectrum fitting method and SEM-EDS analysis to study the destruction mechanism of oxidation zinc varistor in the single pulse and multi-pulse impact conditions, and established a prediction model of MOV crystallinity using varistor voltage (UimA) and leakage current (Iie) as independent variables. Studies showed that:the time interval between pulses had a great influence on the life span of the MOV. In a single pulse impact destruction experiment, the Bi2O3 and Bii2Zn02o in spinel would be converted with each other. There existed MOV damaged differences under the impact of the multi-pulses, some destruction was similar to that of single pulse, some temperature rises of MOV would cause the volatilization of BJ2O3 under a large current surge and the perforation damages of the MOV were caused. But in any impact conditions, the essence of the MOV destruction under any impact condition was each internal microscopic internal components gradually changed from crystalline state to semi-crystalline state process.For the matching problem of each valve block in the MOV multi-chip parallel connection during the impact aging process, this article used impact experiment, infrared thermometer temperature measurement, SEM scanning electron microscopy analysis characterization and other experimental means was used to study the changes of temperature differences of the MOV multi-chip parallel connection during the impact aging process. Studies showed that under a long-term surge impact, each MOV in the parallel body had a different damage condition. MOV with a relative serious destruction would even show transgranular and destructive phenomena, which would cause the resistance of the destructed MOV to produce a great difference compared to the resistance of other MOV. When the MOV was subjected to surges again, it would absorb more of the impact current, which would result in different surge currents of each MOV, resulting in a temperature difference. According to this phenomenon, an embedded multi-point wireless temperature monitoring system was designed. The system can determine the matching condition and the overall extent of the aging of each MOV in the SPD, and has features of being strong in target, real-time and high efficient. |
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